Time delay circuits are well known in the art, but circuits for producing long delays in bipolar circuit technology are difficult to achieve, requiring complex circuitry or processes.
U.S. Pat. No. 3,991,322, filed June 30, 1975, describes a delay circuit utilizing bucket brigade and sample and hold circuits requiring timing pulses.
In U.S. Pat. No. 3,466,469, filed Aug. 19, 1966, a circuit is taught which includes a timing capacitor connected to a PNP-NPN transistor pair with means for providing a linear discharge of the capacitor. Regenerative action of the transistor pair provides an indication of the end of the timing period.
U.S. Pat. No. 3,887,823, filed Dec. 18, 1973, discloses a pulse delay circuit including a differential amplifier having a resistor-capacitor time constant circuit connected to the base of one of the amplifier transistors.